The present invention relates to a process for producing a micro Fresnel lens having fine concentric rings formed on the surface as stepped setbacks.
Conventional optical lenses are manufactured by grinding and polishing glass, plastic and other transparent blanks to give a convex or concave surface of the desired radius. Therefore, the physical constants of an optical lens such as numerical aperture (NA), focal length and F number can only be determined by the lens material and the polishing of transparent blanks such as glass and plastics.
The conventional method of preparing a glass lens is shown in FIG. 1; a glass lens blank 2 fixed on a table 1 is capped with a polishing mold 3 which is rotated about its axis, with an abrasive and water being kept supplied, to polish the blank and produce a glass lens having the desired curvature and spherical surface.
An example of the conventional method for preparing a plastic lens is shown in FIG. 2; a plastic lens blank 5 fixed on the bench of a numerically controlled lathe is ground with a cutting tool 6 by proper numeric control so as to produce a plastic lens having the desired curvature and spherical surface.
As shown above, the conventional methods for producing optical lenses must depend on the skill of experienced operators, and the low cost-effectiveness of these methods has long been one of the greatest concerns to the industry.
Lens aberrations such as chromatic aberration, astigmatism, field curvature and sperhical aberration cannot be well corrected by the physical constants of lens. Chromatic aberration is conventionally corrected by assembling a plurality of lenses, but astigmatism, field curvature and spherical aberration can only be reduced by polishing the lens blank to a precise curvature and spherical surface.